Hispanic Americans (HA) exhibit a three- to fivefold excess prevalence of type 2 diabetes compared to non-Hispanic white (NHW) Americans. Insulin resistance plays a central role in the pathophysiology of type 2 diabetes. Studies have shown that across a wide range of ages, both HA males and females demonstrate greater levels of insulin resistance compared to NHW. It is now well recognized that physical inactivity is associated with insulin resistance, and that exercise improves insulin sensitivity. Interestingly, HA exhibit lower levels of aerobic fitness and chronic physical activity compared to NHW, yet few studies have examined the role that low levels of physical fitness may play in explaining the observed ethnic differences in insulin resistance. The specific causes of insulin resistance in HA are unknown, but it is possible that impairments in the insulin signaling cascade resulting from low levels of physical activity/fitness contribute to this phenomenon. For this doctoral project, we propose a cross-sectional approach to determine: (a) whether or not differences in insulin sensitivity exist between HA and NHW adults, after controlling for levels of cardiorespiratory fitness; and (b) to determine whether or not, at a given level of cardiorespiratory fitness, Mexican Americans and non-Hispanic whites exhibit similar levels of insulin signaling pathway intermediates. Young, non-obese, HA and NHW men and women will be matched across a wide range of levels of aerobic fitness, with ethnic comparisons of insulin sensitivity and skeletal muscle insulin signaling intermediates made across these fitness levels. These findings will have profound implications for public health initiatives aimed at improving Hispanic health.